Aluminum airfoil

ABSTRACT

A method of making an aluminum airfoil includes brazing a first airfoil piece and a second airfoil piece together using a braze material that includes an element selected from magnesium and zinc, to form a braze joint between the first airfoil piece and the second airfoil piece. At least one of the first airfoil piece or the second airfoil piece has an aluminum alloy composition that includes greater than 0.8% by weight of zinc.

BACKGROUND

Airfoils are known and used in machines, such as gas turbine engines. Inan engine, an airfoil may be made of any of various different types ofmaterials, depending upon the operating conditions that the airfoil willbe exposed to. Airfoils in relatively cool portions of the engine, suchas the fan and compressor sections, can utilize different materials thanin relatively hot portions of the engine, such as the turbine section.As an example, certain aluminum or titanium alloys can be used in coolerportions of the engine. For aluminum alloys, there are a wide variety ofcompositions, each with specific processing limitations that must be metin order to obtain the optimal properties of the alloy. As an example,exposure to elevated processing temperatures can over-age the aluminumalloy and thereby debit the strength and other properties. Given theshape and design requirements of an airfoil, and the processinglimitations of aluminum alloys, it has not been possible to use certainaluminum alloys for airfoils.

SUMMARY

A disclosed method of making an aluminum airfoil according to anexemplary aspect of the present disclosure includes brazing a firstairfoil piece and a second airfoil piece together using a braze materialthat includes an element selected from a group consisting of magnesiumand zinc, to form a braze joint between the first airfoil piece and thesecond airfoil piece. At least one of the first airfoil piece and thesecond airfoil piece has an aluminum alloy composition comprisinggreater than 0.8% by weight of zinc.

In a further non-limiting embodiment of any of the foregoingembodiments, at least one of the first airfoil piece and the secondairfoil piece includes an airfoil suction side surface or an airfoilpressure side surface.

In a further non-limiting embodiment of any of the foregoingembodiments, the aluminum alloy composition includes greater than 4% byweight of the zinc.

In a further non-limiting embodiment of any of the foregoingembodiments, the aluminum alloy composition includes greater than 5% byweight of the zinc.

In a further non-limiting embodiment of any of the foregoingembodiments, the aluminum alloy composition includes greater than 7% byweight of the zinc.

In a further non-limiting embodiment of any of the foregoingembodiments, the brazing of the first airfoil piece and the secondairfoil piece encloses a hollow cavity between the first airfoil pieceand the second airfoil piece.

In a further non-limiting embodiment of any of the foregoingembodiments, the brazing includes heating the first airfoil piece, thesecond airfoil piece and the braze material at a temperature that is450° C.-550° C.

A further non-limiting embodiment of any of the foregoing embodimentsincludes brazing in a vacuum environment.

In a further non-limiting embodiment of any of the foregoingembodiments, the brazing of the first airfoil piece and the secondairfoil piece includes compressing and heating the first airfoil pieceand the second airfoil piece in a die.

In a further non-limiting embodiment of any of the foregoingembodiments, the first airfoil piece has the aluminum alloy compositionand the second airfoil piece has a non-aluminum alloy composition and analuminum layer that forms the braze joint with the braze material.

In a further non-limiting embodiment of any of the foregoingembodiments, the braze material includes 40 to 65 weight percent zincand a balance of magnesium.

In a further non-limiting embodiment of any of the foregoingembodiments, the braze material includes 93 to 100% by weight of zincand a balance of magnesium.

In a further non-limiting embodiment of any of the foregoingembodiments, the braze material includes greater than 54% by weight zincand a balance of aluminum.

A aluminum airfoil according to an exemplary aspect of the presentdisclosure includes a first airfoil piece and a second airfoil piecebonded to the first airfoil piece at a braze joint that includes anelement selected from a group consisting of magnesium and zinc. At leastone of the first airfoil piece and the second airfoil piece has analuminum alloy composition comprising greater than 0.8% by weight ofzinc.

In a further non-limiting embodiment of any of the foregoingembodiments, the aluminum alloy composition includes greater than 4% byweight of the zinc.

A further non-limiting embodiment of any of the foregoing embodimentsinclude a hollow cavity between the first airfoil piece and the secondairfoil piece.

In a further non-limiting embodiment of any of the foregoingembodiments, at least one of the first airfoil piece and the secondairfoil piece includes an airfoil pressure side surface or an airfoilsuction side surface.

A gas turbine engine according to an exemplary aspect of the presentdisclosure includes a fan, a compressor section downstream from the fan,a combustor in fluid communication with the compressor section, and aturbine section in fluid communication with the combustor. At least oneof the fan or the compressor section includes an aluminum airfoil thathas a first airfoil piece and a second airfoil piece bonded to the firstairfoil piece at a braze joint that includes an element selected from agroup consisting of magnesium and zinc. At least one of the firstairfoil piece and the second airfoil piece has an aluminum alloycomposition comprising greater than 0.8% by weight of zinc.

In a further non-limiting embodiment of any of the foregoingembodiments, the aluminum alloy composition includes greater than 4% byweight of the zinc.

A further non-limiting embodiment of any of the foregoing embodimentsincludes a hollow cavity between the first airfoil piece the secondairfoil piece.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the disclosed examples willbecome apparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

FIG. 1 shows an example gas turbine engine.

FIG. 2 illustrates an example aluminum airfoil.

FIG. 3 illustrates a cross-sectional view of the aluminum airfoil ofFIG. 2.

FIG. 4A illustrates a portion of aluminum airfoil pieces in a method ofmaking an aluminum airfoil.

FIG. 4B illustrates aluminum airfoil pieces in a method of making analuminum airfoil.

FIG. 4C illustrates aluminum airfoil pieces in a method of making analuminum airfoil.

FIG. 4D illustrates aluminum airfoil pieces in a method of making analuminum airfoil.

FIG. 5 illustrates another cross-sectional view of an aluminum airfoil

FIG. 6 illustrates a portion of a non-aluminum alloy airfoil piecebefore brazing to an aluminum airfoil piece.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. Alternative engines mightinclude an augmentor section (not shown), among other systems orfeatures. The fan section 22 drives air along a bypass flowpath F whilethe compressor section 24 drives air along a core flowpath C forcompression and communication into the combustor section 26 and thenexpansion through the turbine section 28. Although depicted as aturbofan gas turbine engine in the disclosed non-limiting embodiment, itshould be understood that the concepts described herein are not limitedto use with turbofans and the teachings may be applied to other types ofturbine engines, including three-spool architectures.

The engine 20 generally includes a low speed spool 30 and a high speedspool 32 mounted for rotation about an engine central longitudinal axisA relative to an engine static structure 36 via several bearing systems38. It should be understood that various bearing systems 38 at variouslocations may alternatively or additionally be provided.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects a fan 42, a low pressure compressor 44 and a low pressureturbine 46. The inner shaft 40 is connected to the fan 42 through ageared architecture 48 to drive the fan 42 at a lower speed than the lowspeed spool 30, for example. The high speed spool 32 includes an outershaft 50 that interconnects a high pressure compressor 52 and highpressure turbine 54. A combustor 56 is arranged between the highpressure compressor 52 and the high pressure turbine 54. The inner shaft40 and the outer shaft 50 are concentric and rotate via bearing systems38 about the engine central longitudinal axis A, which is collinear withtheir longitudinal axes.

The core airflow C is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The turbines 54, 46 rotationally drive therespective low speed spool 30 and high speed spool 32 in response to theexpansion.

FIG. 2 illustrates an example aluminum airfoil 42 a, which in thisexample is one of a plurality of airfoil blades or vanes in the fan 42of the engine 20. As will be described, the aluminum airfoil 42 a ismade of, at least in part, a brazed, high strength aluminum alloy.Although the aluminum airfoil 42 a is described herein with reference tothe fan 42, the aluminum airfoil 42 a can alternatively be an airfoilblade or vane in the compressor section 24 of the gas turbine engine 20.

As schematically shown, the aluminum airfoil 42 a includes an airfoilsection 70 and a root section 72 for mounting the aluminum airfoil 42 aon a rotor hub. As shown in a cross-sectional view through the airfoilsection 70 in FIG. 3, the airfoil section 70 generally has a wing-likeshape that provides a lift force via Bernoulli's principle such that theairfoil section 70 includes a pressure side surface 74 and an opposedsuction side surface 76.

Referring to FIG. 3, the airfoil section 70 includes a first airfoilpiece 70 a and a second airfoil piece 70 b that is bonded to the firstairfoil piece 70 a at a braze joint 78 located approximately along theneutral axis of the airfoil. As will be described in further detailbelow, the braze joint 78 includes an element selected from magnesiumand zinc, which assists in bonding the first airfoil piece 70 a and thesecond airfoil piece 70 b together. That is, the braze joint 78 includesmagnesium, zinc or both in a higher concentration than in other portionsof the first airfoil piece 70 a and the second airfoil piece 70 b.

In the illustrated example in FIG. 3, the first airfoil piece 70 a andthe second airfoil piece 70 b are bonded together. The first airfoilpiece 70 a includes the pressure side surface 74 and the second airfoilpiece 70 b includes the suction side surface 76. Thus, in this example,the two pieces 70 a and 70 b form the complete airfoil shape. It is tobe understood that in other embodiments, the pieces 70 a and 70 b maynot form the complete airfoil shape and additional pieces can be used topartially or fully form the airfoil shape.

In this embodiment shown in FIG. 3, the first airfoil piece 70 a and thesecond airfoil piece 70 b are shaped such that upon brazing of thepieces 70 a and 70 b, there is a cavity 84 enclosed between the pieces70 a and 70 b. Thus, the airfoil section 70 is hollow, to reduce weightand/or provide mistuning of the airfoil. Additionally, the first airfoilpiece 70 a and the second airfoil piece 70 b each may include a seriesof “pockets” that form a portion of the cavities 84. In another example(see FIG. 5), the first airfoil piece 70 a includes similar “pockets”that form cavities 84 and the second airfoil piece 70 b is a cover overthe pockets.

Optionally, the airfoil section 70 includes an insert 86 (shownschematically in FIGS. 3 and 5) located within the cavity 84. Forexample, the insert 86 is a structural piece that reinforces the hollowstructure of the airfoil section 70. In embodiments, the insert 86includes a spar, foam material or both that structurally supports one ormore of the pieces 70 a and 70 b.

In one embodiment, as shown in FIGS. 3 and 5, the insert 86 is metallicand is also bonded with the first airfoil piece 70 a, the second airfoilpiece 70 b or both at braze joints 78′. Thus, the insert 86 is alsoconsidered herein to be an airfoil piece.

As an indicated above, the airfoil section 70 is made, at least in part,by a high strength aluminum alloy. In one example, at least one of thefirst airfoil piece 70 a, the second airfoil piece 70 b or the insert 86is made of a high strength aluminum alloy composition that includesgreater than 0.8% by weight of zinc. In a further example, the aluminumalloy composition is a 7000 series aluminum alloy. In further examples,the aluminum alloy composition includes greater than 4% by weight of thezinc, greater than 5% by weight of the zinc or greater than 7% by weightof the zinc. In further embodiments, the first airfoil piece 70 a, thesecond airfoil piece 70 b and the insert 86 are all made of the aluminumalloy composition. In other embodiments, at least one of the firstairfoil piece 70 a, the second airfoil piece 70 b or the insert 86 ismade of a different aluminum alloy composition or a non-aluminum alloycomposition.

At least due in part to the presence of the zinc in the aluminum alloycomposition, the aluminum alloy presents challenges in processing toform a reliable airfoil. For example, one challenge is braze bonding ofthe aluminum alloy composition. Typical braze materials, such asaluminum-silicon materials, that are generally used to braze aluminumstructures melt at significantly higher temperatures than the meltingpoint of the zinc-containing aluminum alloy composition of the aluminumairfoil 42 a. Thus, as will be described below with regard to a methodof making the aluminum airfoil 42 a, a braze material that includes atleast one of relatively low melting temperature elements of magnesiumand zinc is used to enable brazing.

FIGS. 4A-D show portions of the first airfoil piece 70 a and the secondairfoil piece 70 b during through a method of making the aluminumairfoil 42 a and braze joint 78. It is to be understood that althoughthis example is described with reference to the first airfoil piece 70 aand the second airfoil piece 70 b, the method is also applicable tobrazing between the first airfoil piece 70 a and the insert 86 and/orthe second airfoil piece 70 b and the insert 86 to form braze joints78′.

As shown in FIG. 4A, the first airfoil piece 70 a and the second airfoilpiece 70 b (each shown in part) are initially separate and distinctpieces. In this example, a braze material 90 is applied onto a surfaceof the first airfoil piece 70 a at a location which is to be brazed tothe second airfoil piece 70 b. Alternatively, the braze material 90 isapplied to the second airfoil piece 70 b or both pieces 70 a and 70 b.In one example, the braze material 90 is applied only to the surfacelocation at which the first airfoil piece 70 a and the second airfoilpiece 70 b are to be bonded together. Thus, the remaining surfaces, suchas the inner surfaces that form the cavity 84, do not include any brazematerial 90 and the amount of braze material 90 used is minimized. Thebraze material 90 may be deposited as a layer using a cathodic arccoating deposition process, although other types of deposition processescan alternatively be used, such as but not limited to electroless,electrolytic, vapor or mechanical (powder). Areas that are not to bebonded can be masked off during deposition of the braze material 90and/or removed by etching, if needed.

In one embodiment, the braze material 90 has a composition that includesmagnesium and zinc. In one example composition, the braze material 90 isa magnesium-zinc alloy that includes 40 to 65 weight percent zinc and abalance of magnesium. In a another example, the braze material 90includes 93 to 100% by weight of zinc and a balance of magnesium. In afurther embodiment, the braze material 90 also includes aluminum. Forexample, the braze material 90 includes greater than 54% by weight zincand a balance of aluminum. In another alternative, relatively pure zincis applied as the braze material 90. It is to be understood that thecomposition of the braze material 90 with regard to the amount ofmagnesium and/or zinc and/or aluminum can be modified to change themelting temperature of the braze material 90. Thus, the meltingtemperature can be modified to meet a temperature target for aparticular brazing process and/or for greater compatibility with thealuminum alloy composition of the airfoil pieces 70 a and 70 b (or 86).

Referring to FIG. 4B, the first airfoil piece 70 a and the secondairfoil piece 70 b are brought together into contact. For example, thefirst airfoil piece 70 a and the second airfoil piece 70 b are broughttogether such that the braze material 90 on the first airfoil piece 70 ais in contact with the bonding surface of the second airfoil piece 70 b.

In a further example, the first airfoil piece 70 a and the secondairfoil piece 70 b are brought together using a metallic vacuum bag. Inthis example, the first airfoil piece 70 a and the second airfoil piece70 b are placed into a vacuum bag, which is then evacuated to a finalnegative pressure with regard to the ambient surrounding environmentalpressure such that the bag presses the airfoil pieces 70 a and 70 btogether. In one example, the final pressure is approximately negativeone atmosphere. The process of evacuating the bag may include flushingthe interior of the bag with an inert gas, such as argon. For instance,the bag is flushed multiple times with argon to substantially remove anyundesired gases, such as oxygen.

Alternatively, the first airfoil piece 70 a and the second airfoil piece70 b are placed into a die that generally conforms to the shape of theairfoil pieces 70 a and 70 b. The die is then closed to press the firstairfoil piece 70 a and the second airfoil piece 70 b together. Similarto the vacuum bag technique, the interior of the die may be flushed withan inert gas, such as argon. The compression of the airfoil pieces 70 aand 70 b in the die also serves to coin the airfoil pieces 70 a and 70 bto assure a proper geometry.

Referring to FIG. 4C, the first airfoil piece 70 a, the second airfoilpiece 70 b and the braze material 90 are then heated at a predeterminedbrazing temperature. In the vacuum bag technique, for example, thevacuum bag and airfoil piece 70 a and 70 b are placed within a heatingchamber. Alternatively, for the die technique, the die is heated at thedesired predetermined brazing temperature.

The predetermined brazing temperature is selected to at least partiallymelt the braze material 90, while the first airfoil piece 70 a and thesecond airfoil piece 70 b remain unmelted. In one example, thepredetermined brazing temperature is 450-550° C. to melt the brazematerial 90 but not melt the aluminum alloy composition of the firstairfoil piece 70 a, the second airfoil piece 70 b or both.

As indicated above, high strength aluminum alloy compositions thatinclude greater than 0.8% by weight of zinc melt at a relatively lowtemperature in comparison to other aluminum alloys. As an example basedupon aluminum alloy 7255, the high strength aluminum alloy melts atapproximately 514° C. Thus, the composition of the braze material 90 isselected such that its melting temperature is lower than the meltingtemperature of the aluminum alloy of the first airfoil piece 70 a, thesecond airfoil piece 70 b or both.

In a further example, the predetermined brazing temperature is above asolutionizing temperature of the aluminum alloy composition of the firstairfoil piece 70 a, the second airfoil piece 70 b or both. Thesolutionizing temperature is the temperature above which any alloyingelements “dissolve” into solid solution with the aluminum. In oneexample, the solutionizing temperature of the aluminum alloy compositionhaving greater than 0.8% by weight of zinc is greater than approximately475° C. Thus, the selected predetermined brazing temperature is abovethe solutionizing temperature such that the brazing process also servesas a solutionizing heat treatment for the aluminum alloy composition.

Referring also to FIG. 4D, as the braze material 90 melts, the magnesiumand/or zinc diffuses into the first airfoil piece 70 a and the secondairfoil piece 70 b. For example, the brazing temperature is held for apredetermined amount of time to adequately diffuse the braze material.In a further example, the hold time is minimized to limit the formationof intermetallic phases. Upon sufficient diffusion, the braze joint 78isothermally solidifies. As an example, the diffusion of the magnesiumand/or zinc from the liquid braze material 90 into the airfoil pieces 70a and 70 b causes the composition of the liquid braze material 90 tochange and isothermally solidify. That is, as the magnesium and/or zincdiffuses, the composition of the braze material 90 changes to acomposition that has a higher melting point.

After solidification of the braze joint 78, the aluminum airfoil 42 a isthen quench cooled. As indicated above, the brazing is conducted at atemperature that is above the solutionizing temperature of the aluminumalloy composition of the first airfoil piece 70 a, the second airfoilpiece 70 b or both. In one example, the rate of cooling is controlled tocontrol precipitation. The cooling rate should be sufficiently high suchthat the aluminum alloy is adequately solution heat-treated to achievethe required properties for a specific application/design.

In a further example, the aluminum airfoil 42 a is cooled using acooling fluid, such as a gas. For instance, argon gas is blown over thealuminum airfoil 42 a at a relatively high rate. In an example based onthe vacuum bag technique, the argon gas is forced onto a metallic bagwhich is in intimate contact with the aluminum airfoil 42 a. Theintimate contact between the metallic bag and the aluminum airfoil 42 ais assured by the negative atmospheric pressure within the metallic bagin which the aluminum airfoil 42 a resides. The intimate contact ensuresrapid cooling of the aluminum airfoil 42 a such that adequate solutionheat-treatment is achieved.

In a further example, the aluminum airfoil 42 a is then furthersubjected to a controlled aging heat treatment to produce a desirableamount of precipitation and thereby strengthen the aluminum alloycomposition. Thus, the brazing process to make the aluminum airfoil 42 asubstantially avoids precipitation so that the later controlled agingheat treatment can be used to produce a desirable microstructure toobtain target final properties of the aluminum airfoil 42 a.

FIG. 5 illustrates another example airfoil section 170 that may be usedas an alternative in the aluminum airfoil 42 a. In this example, theairfoil section 170 also includes the first airfoil piece 70 a and thesecond airfoil piece 70 b. However, a sheath 96 is bonded to the firstairfoil piece 70 a at the leading end 80. In this example, the sheath 96is made of a non-aluminum material, such as a titanium alloy or steel.Typically, dissimilar metals or metal alloys cannot be brazed together.However, as shown in FIG. 6, the portions of the sheath 90 that are tobe bonded to the first airfoil piece 70 a and the second airfoil piece70 b include an aluminum layer 98 that allows the sheath 96 to be brazedto the first airfoil piece 70 a and the second airfoil piece 70 b.Alternatively, if the non-aluminum material of the sheath 96 iscompatible with the braze material 90 such that the braze material 90wets the non-aluminum material upon melting, the aluminum layer 98 canbe excluded.

FIG. 6 shows portions of the sheath 96 and the first airfoil piece 70 aprior to brazing. Similar to the brazing process as described withreference to FIG. 4A, the first airfoil piece 70 a is provided with abraze material 90 for brazing/bonding with the sheath 96. The sheath 96includes, at least on surfaces that are to be bonded, the aluminum layer98. In embodiments, the aluminum layer 98 is relatively pure aluminum oran aluminum alloy that includes a greater than 0.8% by weight of zinc,similar to the composition used for the first airfoil piece 70 a in thisexample. Alternatively, the braze material 90 can be applied on top ofthe aluminum layer 98 on the sheath 96. Similar to the brazing processas described with reference to FIGS. 4B-D, the first airfoil piece 70 aand the sheath 96 are then brought together, heated, and cooled to forma braze joint 178 (FIG. 5). In this regard, the aluminum layer 98 on thedissimilar metal of the sheath 96 permits the sheath 96 and the airfoilpiece 70 a to be bonded together. In a further example, the brazing ofthe sheath 96 is conducted concurrently with the brazing to form brazejoints 78, as described above.

Although a combination of features is shown in the illustrated examples,not all of them need to be combined to realize the benefits of variousembodiments of this disclosure. In other words, a system designedaccording to an embodiment of this disclosure will not necessarilyinclude all of the features shown in any one of the Figures or all ofthe portions schematically shown in the Figures. Moreover, selectedfeatures of one example embodiment may be combined with selectedfeatures of other example embodiments.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthe essence of this disclosure. The scope of legal protection given tothis disclosure can only be determined by studying the following claims.

What is claimed is:
 1. A method of making an aluminum airfoil, themethod comprising: brazing a first airfoil piece and a second airfoilpiece together using a braze material that includes an element selectedfrom a group consisting of magnesium and zinc, to form a braze jointbetween the first airfoil piece and the second airfoil piece, and atleast one of the first airfoil piece and the second airfoil piece has analuminum alloy composition comprising greater than 0.8% by weight ofzinc.
 2. The method as recited in claim 1, wherein at least one of thefirst airfoil piece and the second airfoil piece includes an airfoilsuction side surface or an airfoil pressure side surface.
 3. The methodas recited in claim 1, wherein the aluminum alloy composition includesgreater than 4% by weight of the zinc.
 4. The method as recited in claim1, wherein the aluminum alloy composition includes greater than 5% byweight of the zinc.
 5. The method as recited in claim 1, wherein thealuminum alloy composition includes greater than 7% by weight of thezinc.
 6. The method as recited in claim 1, wherein the brazing of thefirst airfoil piece and the second airfoil piece enclose a hollow cavitybetween the first airfoil piece and the second airfoil piece.
 7. Themethod as recited in claim 1, wherein the brazing includes heating thefirst airfoil piece, the second airfoil piece and the braze material ata temperature that is 450° C.-550° C.
 8. The method as recited in claim1, including brazing in a vacuum environment.
 9. The method as recitedin claim 1, wherein the brazing of the first airfoil piece and thesecond airfoil piece includes compressing and heating the first airfoilpiece and the second airfoil piece in a die.
 10. The method as recitedin claim 1, wherein the first airfoil piece has the aluminum alloycomposition and the second airfoil piece has a non-aluminum alloycomposition and an aluminum layer that forms the braze joint with thebraze material.
 11. The method as recited in claim 1, wherein the brazematerial includes 40 to 65 weight percent zinc and a balance ofmagnesium.
 12. The method as recited in claim 1, wherein the brazematerial includes 93 to 100% by weight of zinc and a balance ofmagnesium.
 13. The method as recited in claim 1, wherein the brazematerial includes greater than 54% by weight zinc and a balance ofaluminum.
 14. A aluminum airfoil comprising: a first airfoil piece; anda second airfoil piece bonded to the first airfoil piece at a brazejoint that includes an element selected from a group consisting ofmagnesium and zinc, and at least one of the first airfoil piece and thesecond airfoil piece has an aluminum alloy composition comprisinggreater than 0.8% by weight of zinc.
 15. The aluminum airfoil as recitedin claim 14, wherein the aluminum alloy composition includes greaterthan 4% by weight of the zinc.
 16. The aluminum airfoil as recited inclaim 14, including a hollow cavity between the first airfoil piece andthe second airfoil piece.
 17. The aluminum airfoil as recited in claim14, wherein at least one of the first airfoil piece and the secondairfoil piece includes an airfoil pressure side surface or an airfoilsuction side surface.
 18. A gas turbine engine comprising: a fan; acompressor section downstream from the fan; a combustor in fluidcommunication with the compressor section; and a turbine section influid communication with the combustor, and at least one of the fan orthe compressor section including an aluminum airfoil that has a firstairfoil piece and a second airfoil piece bonded to the first airfoilpiece at a braze joint that includes an element selected from a groupconsisting of magnesium and zinc, and at least one of the first airfoilpiece and the second airfoil piece has an aluminum alloy compositioncomprising greater than 0.8% by weight of zinc.
 19. The gas turbineengine as recited in claim 18, where the aluminum alloy compositionincludes greater than 4% by weight of the zinc.
 20. The gas turbineengine as recited in claim 18, including a hollow cavity between thefirst airfoil piece the second airfoil piece.